permutes as rotates of length 2, and make any rotate active
over any subset of lane bits. This is hard, and requires general
permute; current intrinsics mean this is only really possible for specific
case by case encodings as presently performed. Intel could produce a general
permute.. would help. IBM did it in VMX.
connect the "Real" default precisoin to a configure flag.
Have RealF, RealD and Real types, where Real is compile target dependent single/double,
RealF is single and RealD is double etc..
